1. THE SECOND LAW OF THERMODYNAMICS

2. Processes occur in a certain direction, and not in the reverse direction.
A process must satisfy both the first and second laws of thermodynamics to proceed.
MAJOR USES OF THE SECOND LAW
The second law may be used to identify the direction of processes.
The second law also asserts that energy has quality as well as quantity. The first law is concerned with the quantity of energy and the transformations of energy from one form to another with no regard to its quality. The second law provides the necessary means to determine the quality as well as the degree of degradation of energy during a process.
The second law of thermodynamics is also used in determining the theoretical limits for the performance of commonly used engineering systems, such as heat engines and refrigerators, as well as predicting the degree of completion of chemical reactions.

3. INTRODUCTION TO THE SECOND LAW
These processes cannot occur even though they are not in violation of the first law.
Transferring heat to a wire will not generate electricity.
Transferring heat to a paddle wheel will not cause it to rotate.

4. THERMAL ENERGY RESERVOIRS
A hypothetical body with a relatively large thermal energy capacity (mass x specific heat) that can supply or absorb finite amounts of heat without undergoing any change in temperature is called a thermal energy reservoir, or just a reservoir.
In practice, large bodies of water such as oceans, lakes, and rivers as well as the atmospheric air can be modeled accurately as thermal energy reservoirs because of their large thermal energy storage capabilities or thermal masses.
A source supplies energy in the form of heat, and a sink absorbs it.

5. HEAT ENGINES The devices that convert heat to work.
They receive heat from a high-temperature source (solar energy, oil furnace, nuclear reactor, etc.).
They convert part of this heat to work (usually in the form of a rotating shaft.)
They reject the remaining waste heat to a low-temperature sink (the atmosphere, rivers, etc.).
They operate on a cycle.
Heat engines and other cyclic devices usually involve a fluid to and from which heat is transferred while undergoing a cycle. This fluid is called the working fluid.
Work can always be converted to heat directly and completely, but the reverse is not true.
A device is needed.
Part of the heat received by a heat engine is converted to work, while the rest is rejected to a sink.

6. Example: A steam power plant
A portion of the work output of a heat engine is consumed internally to maintain continuous operation.

7. Thermal efficiency
Is a measure of how efficiently a heat engine converts the heat that it receives to work.
Some heat engines perform better than others (convert more of the heat they receive to work).
Even the most efficient heat engines reject almost one-half of the energy they receive as waste heat.

8. Thermal efficiency Qout = Magnitude of the energy wasted, ≠ 0.
Qout = Magnitude of the energy wasted, ≠ 0.
Qin = Magnitude of the input energy.
QH = Magnitude of heat transfer between the cyclic device and the high temperature medium at temperature, TH.
QL = Magnitude of heat transfer between the cyclic device and the lower temperature medium at temperature, TL.

9. Example 1
A heat engine has a total heat input of 1.3 kJ and a thermal efficiency of 35%. How much work will it produce?
Solution:

10. Can we save Qout?
In a steam power plant, the condenser is the device where large quantities of waste heat is rejected to rivers, lakes, or the atmosphere.
Can we not just take the condenser out of the plant and save all that waste energy?
The answer is, unfortunately, a firm no for the simple reason that without a heat rejection process in a condenser, the cycle cannot be completed.
A heat-engine cycle cannot be completed without rejecting some heat to a low-temperature sink.
Every heat engine must waste some energy by transferring it to a low-temperature reservoir in order to complete the cycle, even under idealized conditions.

11. Example 2
A steam power plant with a power output of 150 MW consumes coal at a rate of 60 tons/h. If the heating value of coal is 30,000 kJ/kg, determine the overall efficiency of this plant.
The heating value of coal, , is given to be 30,000 kJ/kg.
Rate of consumption, , is 60 tons/h, which is equal to 60,000kg/h.
The rate of heat supply to this power plant is
sink HE
60 t/h
coal
Furnace
150 MW
Then the thermal efficiency of the plant becomes

12. Kelvin–Planck Statement
The Second Law of Thermodynamics:
Kelvin–Planck Statement
It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work.
No heat engine can have a thermal efficiency of 100 percent, or as for a power plant to operate, the working fluid must exchange heat with the environment as well as the furnace.
The impossibility of having a 100% efficient heat engine is not due to friction or other dissipative effects. It is a limitation that applies to both the idealized and the actual heat engines.
A heat engine that violates the Kelvin–Planck statement of the second law.

13. REFRIGERATORS AND HEAT PUMPS
The transfer of heat from a low-temperature medium to a high-temperature one requires special devices called refrigerators.
Refrigerators, like heat engines, are cyclic devices.
The working fluid used in the refrigeration cycle is called a refrigerant.
The most frequently used refrigeration cycle is the vapor-compression refrigeration cycle.
Basic components of a refrigeration system and typical operating conditions.
In a household refrigerator, the freezer compartment where heat is absorbed by the refrigerant serves as the evaporator, and the coils usually behind the refrigerator where heat is dissipated to the kitchen air serve as the condenser.

14. PoO: Refrigerator
Consist of 4 main component: compressor, condenser, expansion valve, evaporator.
The refrigerant enters the compressor as a vapor and compressed to the condenser pressure.
It leaves the compressor at a relatively high temperature and cools down and condenses as it flow through the coils of the condenser by rejecting heat the surrounding medium.
It then enters capillary tube where its pressure and temperature drops drastically due to the throttling effect.
The low-temperature refrigerant then enters the evaporator, where it evaporates by absorbing heat from the refrigerated space.
The cycle is complete as the refrigerant leaves the evaporator and reenters the compressor.

15. Coefficient of Performance
The efficiency of a refrigerator is expressed in terms of the coefficient of performance (COP).
The objective of a refrigerator is to remove heat (QL) from the refrigerated space.
The objective of a refrigerator is to remove QL from the cooled space.
Can the value of COPR be greater than unity?
It can be greater or less than unity depending on the ratio QH/QL

16. Heat Pumps The objective of a heat pump is to
supply heat QH into the warmer space.
The work supplied to a heat pump is used to extract energy from the cold outdoors and carry it into the warm indoors.
Can the value of COPHP be lower than unity? No
What does COPHP=1 represent?
for fixed values of QL and QH

17. When installed backward, an air conditioner functions as a heat pump.
Most heat pumps in operation today have a seasonally averaged COP of 2 to 3.
Most existing heat pumps use the cold outside air as the heat source in winter (air-source HP).
In cold climates their efficiency drops considerably when temperatures are below the freezing point.
In such cases, geothermal (ground-source) HP that use the ground as the heat source can be used.
Such heat pumps are more expensive to install, but they are also more efficient.
Air conditioners are basically refrigerators whose refrigerated space is a room or a building instead of the food compartment.
The COP of a refrigerator decreases with decreasing refrigeration temperature.
Therefore, it is not economical to refrigerate to a lower temperature than needed.
When installed backward, an air conditioner functions as a heat pump.
Energy efficiency rating (EER): The amount of heat removed from the cooled space in Btu’s for 1 Wh (watthour) of electricity consumed.

18. The Second Law of Thermodynamics: Clasius Statement
It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body.
It states that a refrigerator cannot operate unless its compressor is driven by an external power source, such as an electric motor.
This way, the net effect on the surroundings involves the consumption of some energy in the form of work, in addition to the transfer of heat from a colder body to a warmer one.
To date, no experiment has been conducted that contradicts the second law, and this should be taken as sufficient proof of its validity.
A refrigerator that violates the Clausius statement of the second law.

19. Equivalence of the Two Statements
Proof that the violation of the Kelvin–Planck statement leads to the violation of the Clausius statement.
The Kelvin–Planck and the Clausius statements are equivalent in their consequences, and either statement can be used as the expression of the second law of thermodynamics.
Any device that violates the Kelvin–Planck statement also violates the Clausius statement, and vice versa.

20. PERPETUAL-MOTION MACHINES
A perpetual-motion machine that violates the second law of thermodynamics (PMM2).
A perpetual-motion machine that violates the first law (PMM1).
Perpetual-motion machine: Any device that violates the first or the second law.
A device that violates the first law (by creating energy) is called a PMM1.
A device that violates the second law is called a PMM2.
Despite numerous attempts, no perpetual-motion machine is known to have worked. If something sounds too good to be true, it probably is.

21. Thank You